Embodiments in accordance with the present invention relate to a disk drive and disk drive control method, and more particularly to a disk drive whose head slider includes a heater for adjusting the clearance between a head element section and recording disk, and a method for controlling the heater.
Devices using various types of media such as optical disks, magnetic tapes, and semiconductor memories are known in the art as data storage devices. Among them, hard disk drives (hereinafter referred to as HDDs) have become popular as storage devices for computers to such an extent that they are one of the storage devices indispensable for today's computer systems. Further, not limited to the computers as described above, HDDs are expanding more and more in application because of their excellent characteristics. For example, HDDs are used for moving picture recording/reproducing devices, car navigation systems, cellular phones, and removable memories for use in digital cameras.
A magnetic disk for use with a hard disk drive (HDD) contains a plurality of concentric data tracks. Each data track contains a plurality of servo data, which includes address information, and a plurality of data sectors, which includes user data. A plurality of data sectors are recorded between servo data. A data write into a data sector and a data read from a data sector are performed when a head element section of a head slider, which is supported by an oscillating actuator, accesses a desired data sector in accordance with the address information included in the servo data.
For an increase in the recording density of the magnetic disk, it is important that the clearance between the magnetic disk and the head element section, which flies over the magnetic disk, be decreased. A number of mechanisms for adjusting the clearance were proposed. In one of the proposed mechanisms, the head slider is provided with a heater, which heats the head element section to adjust the clearance (refer, for instance, to Japanese Patent Laid-Open No. 20635/1993). This technology is hereinafter referred to as the TFC (Thermal Fly height Control) technology. The TFC technology supplies a current (power) to the heater for heat generation, and protrudes the head element section by means of thermal expansion. This makes it possible to reduce the clearance between the magnetic disk and head element section.
Two types of head element section protrusion occur during a normal operation. More specifically, the head element section protrudes due to a rise in the environmental temperature (this is referred to as environmental protrusion). The head element section also protrudes when a write element generates heat during a data write (this is referred to as write protrusion). The write element generates a magnetic field to write data onto the magnetic disk when a current flows to a coil. The resulting write current causes the write element to generate heat.
When a hard disk drive is to be designed, the clearance is determined to avoid collision between the head element section and magnetic disk while considering the environmental protrusion, which is based on the environmental temperature, and write protrusion, which is based on the write current. Therefore, adequate read performance can be obtained in a high-temperature environment due to environmental protrusion; however, adequate read performance may not be obtained in a low-temperature environment. Further, the clearance provided at an initial stage of a data write may differ from the clearance provided later due to write protrusion so that an inadequate write results at the initial stage of a data write (poor overwrite).
The TFC technology reduces the clearance between the head element section and magnetic disk to solve a problem in which the read performance deteriorates due to environmental temperature changes and a poor overwrite occurs at the initial stage of a data write. On the other hand, the TFC technology protrudes the head element section as compared to the normal situation. Therefore, it is likely to incur collision between the magnetic disk and head element section. Consequently, it is extremely important during the use of the TFC technology that the timing for energizing the heater to protrude the head element section be properly controlled.
As described earlier, hard disk drives are used for various applications. An external impact is often applied to the hard disk drives particularly when they are built in a notebook PC, digital camera, or other portable electronic device. When an external impact is applied to a hard disk drive, the actuator may vibrate, thereby causing the head element section to collide against the magnetic disk. If the TFC technology protrudes the head element section while the actuator is significantly vibrating, the probability of collision between the head element section and magnetic disk increases.
Impact-induced actuator vibration does not end immediately. Residual vibration of the actuator continues subsequently. The head element section is positioned near the magnetic disk during such a residual vibration period. Therefore, if the head element section is protruded, the probability of collision between the head element section and magnetic disk increases. Meanwhile, it is demanded from the viewpoint of hard disk drive performance that the heater be turned ON as soon as possible to start a data write/data read operation.